Processing script in IE8

Why processing.js is not running in IE8? For example the demo given in processing document http://processingjs.org开发者_C百科/learning/topic/rollover

IE8 and before do not support <canvas> - no Internet Explorer before version 9 will work with Processing.js because of this.

I certainly agree with Mike regarding the limitations of IE8 and lower, but apparently it is still possible, though it doesn't work right out of the box. See related question "Has anyone got processing.js working in IE?"